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Also see Kibi, mebi, gibi, tebi,
pebi, and all that, which are relatively new prefixes designed to
express power-of-two multiples.
Kilo, mega, giga, tera, and peta are among the list of prefixes
that are used to denote the quantity of something, such as, in
computing and telecommunications, a class or a bit. Sometimes called
prefix multipliers, these prefixes are also used in
electronics and physics. Each multiplier consists of a one-letter
abbreviation and the prefix that it stands for.
In communications, electronics, and physics, multipliers are
defined in powers of 10 from 10-24 to 1024,
proceeding in increments of three orders of magnitude
(103 or 1,000). In IT and data storage, multipliers are
defined in powers of 2 from 210 to 280,
proceeding in increments of ten orders of magnitude (210
or 1,024). These multipliers are denoted in the following table.
| Prefix |
Symbol(s) |
Power of 10 |
Power of 2 |
| yocto- |
y |
10-24 * |
-- |
| zepto- |
z |
10-21 * |
-- |
| atto- |
a |
10-18 * |
-- |
| femto- |
f |
10-15 * |
-- |
| pico- |
p |
10-12 * |
-- |
| nano- |
n |
10-9 * |
-- |
| micro- |
m |
10-6 * |
-- |
| milli- |
m |
10-3 * |
-- |
| centi- |
c |
10-2 * |
-- |
| deci- |
d |
10-1 * |
-- |
| (none) |
-- |
100 |
20 |
| deka- |
D |
101 * |
-- |
| hecto- |
h |
102 * |
-- |
| kilo- |
k or K ** |
103 |
210 |
| mega- |
M |
106 |
220 |
| giga- |
G |
109 |
230 |
| tera- |
T |
1012 |
240 |
| peta- |
P |
1015 |
250 |
| exa- |
E |
1018 * |
260 |
| zetta- |
Z |
1021 * |
270 |
| yotta- |
Y |
1024 * |
280 |
| * Not generally used to express data speed |
| ** k = 103 and K =
210 |
Examples of quantities or phenomena in which power-of-10 prefix
multipliers apply include frequency (including computer clock
speeds), physical mass, power, energy, electrical voltage, and
electrical current. Power-of-10 multipiers are also used to define
binary data speeds. Thus, for example, 1 kbps (one kilobit per
second) is equal to 103, or 1,000, bps (bits per second);
1 Mbps (one megabit per second) is equal to 106, or
1,000,000, bps. (The lowercase k is the technically correct symbol
for kilo- when it represents 103, although the uppercase
K is often used instead.)
When binary data is stored in memory or fixed media such as a
hard drive, diskette, ZIP disk, tape, or CD-ROM, power-of-2
multipliers are used. Technically, the uppercase K should be used
for kilo- when it represents 210. Therefore 1 KB (one
kilobyte) is 210, or 1,024, bytes; 1 MB (one megabyte) is
220, or 1,048,576 bytes.
The choice of power-of-10 versus power-of-2 prefix multipliers
can appear arbitrary. It helps to remember that in common usage,
multiples of bits are almost always expressed in powers of 10, while
multiples of bytes are almost always expressed in powers of 2.
Rarely is data speed expressed in bytes per second, and rarely is
data storage or memory expressed in bits. Such usages are considered
improper. Confusion is not likely, therefore, provided one adheres
strictly to the standard usages of the terms bit and byte.
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